This invention relates to electronically controlled actuators such as electronic servo-controlled motors and, more particularly, to a starting circuit for stabilizing the starting performance of such an actuator.
A motor with which stable and constant speed rotation can be obtained without being affected by changes of the load or other external disturbances is desired for such purposes as driving a capstan in a tape recorder. Various motors of this sort have been developed, and an example of them is a DC servo-motor which includes a pulse count type frequency-to-voltage (F/V) converter in its servo-loop. A motor control apparatus which is applicable for use with this type of servo-motor is disclosed in Japanese Patent Publication No. 32126/79. The servo-loop of the disclosed motor control apparatus mentioned above includes an integration capacitor. This integration capacitor is essential for the stable operation of the servo-loop. When the servo-loop is in operation, a quantity of charge within a constant range is charged into and discharged from the integration capacitor.
The power supply of the apparatus where the servo-motor as mentioned above is employed is turned on and off entirely arbitrarily. It is now assumed that an uncertain quantity of charge remains in the integration capacitor when the power supply of the motor control apparatus is turned on after it has been turned off once. In this case, the starting performance of the motor after the power supply is turned on fluctuates due to the aforementioned uncertain quantity of residual charge; that is, the starting performance of the apparatus is subject to fluctuations in an uncertain fashion depending upon the on-off operation of the power supply switch.
In order to solve this problem, it has been proposed to connect a diode in parallel with the integration capacitor for discharging the residual charge after the turning-off of the power supply. In this case, however, when the voltage across the integration capacitor becomes lower than the forward voltage drop VF of the diode, the residual charge in the integration capacitor can no longer be discharged. Therefore, this parallel diode connection method cannot give a sufficient solution to the above problem.